1. Field of the Invention
The present invention relates generally to modem communications, and more particularly, to the scaling of modem transfer capacity.
2. Description of the Related Art
As the complexity of online content grows, many users find that typical connections, such as a 28.8 KBPS modem, are simply not fast enough. Even newer modems allowing communication speeds of 56.6 KBPS seem slow in some applications. A common bottleneck in online applications, such as the Internet, is telecommunications bandwidth. Projected demand for additional services, such as video-on-demand, teleconferencing, interactive TV, and the like is likely to exacerbate the bandwidth problem.
One telecommunications protocol designed to alleviate the bandwidth problem is described in the asymmetric digital subscriber line (ADSL) standard, ANSI T1.413 Issue 2, entitled, xe2x80x9cInterface Between Networks and Customer Installationxe2x80x94Asymmetric Digital Subscriber Line (ADSL) Metallic Interface, Rev. R1, dated May 4, 1997 incorporated herein by reference in its entirety.
The technology employed in T1.413 type modems is termed discrete multi-tone. The standard defines 256 discrete tones. Each tone represents a carrier signal that can be modulated with a digital signal for transmitting data. The specific frequency for a given tone is N=4.3125 KHz times the tone number. Tones 1-7 are reserved for voice band and guard band (i.e., tone 1 is the voice band and tones 2-7 are guard bands). Data is not transmitted near the voice band to allow for simultaneous voice and data transmission on a single line. The guard band helps isolate the voice band from the ADSL data bands. Typically, a splitter may be used to isolate any voice band signal from the data tones. Tones 8-32 are used to transmit data upstream (i.e., from the user), and tones 33-256 are used to transmit data downstream (i.e., to the user). Alternatively, all the data tones 8-256 may be used for downstream data, and upstream data present on tones 8-32 would be detected using echo cancellation. Because more tones are used for downstream communication than for upstream communication, the transfer is said to be asynchronous.
Through a training procedure, the modems on both sides of the connection sense and analyze which tones are clear of impairments in the telephone line. Each tone that is clear is used to carry information. Accordingly, the maximum capacity is set by the quality of the telephone connection. The data rate defined by the ADSL specification, assuming all tones are clear of impairments, is about 8 MBPS downstream and about 640 KBPS upstream.
FIG. 1 illustrates the bandwidth requirements for an ADSL modem using these parameters. To support the frequency bandwidth shown in FIG. 1, the ADSL modem must have an analog sampling rate of at least 2.2E+6 samples per second.
The ADSL modem described above has a high bandwidth for transmitting data, but is inflexible. All potential installations might not require the same bandwidth. Also, some users may require a more balanced bandwidth ratio. In addition, due to the algorithm processing requirements, storage requirements, power consumption, gate count, analog sample converter rate, and physical size required to support the bandwidth shown in FIG. 1, the modem is costly, which may preclude its use for certain applications.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
In one aspect of the present invention, a communications system includes a plurality of lines, a modulator/demodulator, a processing unit, and a negotiation unit. The modulator/demodulator is coupled to the lines and adapted to communicate data over the lines using a plurality of tone sets. Each tone set is associated with a particular line. The processing unit has an amount of available processing resources for supporting the modulator/demodulator and is adapted to generate resource availability data based on the amount of available processing resources. The negotiation unit is adapted to receive the resource availability data from the processing unit and determine a subset of available tones within each tone set based on the resource availability data. The modulator/demodulator is adapted to communicate data on each line using the subset of available tones.
In another aspect of the present invention, a method is provided for allocating the resources of a communications system. The method includes determining an amount of available processing resources for a processing unit. The processing unit is adapted to support a plurality of connections over a plurality of lines. Each connection has an associated tone set for communicating data. A first connection is established over a first line. A first portion of the available processing resources is allocated to the first connection. A first tone range is determined based on the first portion. The first tone range is a subset of the tone set associated with the first line.